Pages: [1]   Go Down
Author Topic: Lowering voltage by a specific amount?  (Read 577 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Newbie
*
Karma: 0
Posts: 12
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I bought a sparkfun laser card (http://www.sparkfun.com/datasheets/Components/Laser-Card.pdf)
It states that the voltage should be 3.1 +/- 10%.  I was trying to figure out how I can lower the voltage from 3.5 (or 5V) to 3.1.  Is there a way to adjust voltage like this?  Or would it be ok to put a diode in the circuit (from what I understand this would lower the voltage by ~.7).
Thanks for any help!
Logged

UK
Offline Offline
Faraday Member
**
Karma: 100
Posts: 4153
Where is your SSCCE?!?!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

It all depends on how much current draw you're looking at, and how precise you want to get the voltage.

You can use an adjustable "Low Drop-Out" voltage regulator to get a precise voltage from the 5v connection.  This would be the most precise way.

Yes, a diode will give a roughly 0.7v drop per diode.  You can't get 3.1v using silicon diodes alone.  A combination of silicon and schottky diodes could be employed, but that would probably cost more than an LDO regulator.

If the current draw is a constant value (say for an LED), then a simple resistor can be used to drop the voltage.  Using Ohm's law you can calculate the value of the resistor to use.
Logged

Get 10% off all 4D Systems TFT screens this month: use discount code MAJENKO10

Offline Offline
Newbie
*
Karma: 0
Posts: 12
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Thanks for the answer.  I was under the impression that resistors lower current, not voltage, guess I was wrong..  Havent heard about schottky diodes, putting it on my list of things to learn
Logged

Grand Blanc, MI, USA
Offline Offline
Faraday Member
**
Karma: 95
Posts: 4093
CODE is a mass noun and should not be used in the plural or with an indefinite article.
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Thanks for the answer.  I was under the impression that resistors lower current, not voltage, guess I was wrong..  Havent heard about schottky diodes, putting it on my list of things to learn

Resistance is the constant of proportionality between voltage and current. See http://en.wikipedia.org/wiki/Ohms_law
Logged

MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

Offline Offline
Full Member
***
Karma: 0
Posts: 162
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Use a germanium diode, like a 1N34A, instead of silicon.   It has a drop of .15 to .3v depending on current.  Perhaps use two.
Logged

Montreal
Offline Offline
Faraday Member
**
Karma: 30
Posts: 2602
Per aspera ad astra.
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Resistor should be o'k for laser, knowing current from the spec. data, do a math : R = ( 5 - 3.1 ) / 35 mA = 54.28 Ohm
Logged

Pages: [1]   Go Up
Jump to: